FIELD OF THE INVENTION
The invention relates to a process for testing, repairing or exchanging nozzles penetrating the bottom of a reactor pressure vessel, wherein each nozzle serves for the introduction of a respective probe of an in-core instrumentation of a water-cooled nuclear reactor.
Depending on the power and type of the nuclear reactor, a greater or lesser number (about 50) of nozzles pass through the bottom of the reactor pressure vessel. The probes, which are fitted with detectors on their free end regions, are made to enter the fuel assemblies during reactor operation. They are therefore exposed to a high level of radioactive radiation. If testing, repairing or exchanging of nozzles is necessary, the fuel assemblies of the reactor core and all of the core internals are removed from the reactor pressure vessel. Before taking out the fuel assemblies, the probes of the in-core instrumentation, which can travel in channels of the fuel assemblies, must be parked outside in guide tubes leading away from the nozzles. Since the detectors are highly contaminated, due to their insertion in the reactor core, an undesired radioactive loading is the consequence.